2009-09-14_GENERAL DOCUMENTS - C1981019

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to 6,560 feet near the northeast corner of the permit area. Valleys that cut into the upland surface are generally narrow, V-shaped, and about 250 to 500 feet deep. The topographic surface north of the proposed East Pit, West Pit and Section 16 Pit mining sites is dominated by two ridges about two miles long, trending north-northeast, bounded by Goodspring, Taylor and Wilson Creeks. The South Taylor Mining area lies north and west of the northward flowing Goodspring Creek, which is paralleled by Colorado Highway 13. The area is also just south of the northward flowing Taylor Creek, which runs adjacent to. the current Section 16 and West Pits. Much of the area is gently sloping upland rangeland from approximately 8,400 feet to 7,900 feet. Much of the area on the perimeter of the South Taylor mining area is steeply sloping, with slopes in excess of 20%. 3.2.5 Geology Geologic information is found in Sections 2.04.6, Maps 7 through 9A, and Exhibit 6 of the PAP. The permit area lies about six miles south of the axis of the Axial Basin Anticline, a large northwest-trending fold found in the southern Uinta region of the Piceance Basin. The anticline structure and corresponding syncline (Collom Syncline) to the south consist of thousands of feet of marine deposited sediments of Cretaceous age. To the south of the anticline, the axis of the Collom Syncline, a downward fold, passes directly through the permit area, trending north 70 degrees west and plunging from 0 to 20 degrees to the North. In the southeastern corner of the permit area, near Streeter Fill, the Collom Syncline is influenced by the Elkhorn Syncline which results in strata having an eastward dip and north-south strike (see Map 7 and Figure 1 in the PAP). There appears to be no evidence of faulting in the permit area; however, linear features that may be fault-related have been observed from aerial photographs. These lineations trend approximately north 70 degrees west, north 45 degrees west and north 30 degrees east, with near vertical inclinations. The coal-bearing strata of interest to the Colowyo operation are stratigraphically located in the Mesaverde Group within the Williams Fork Formation of upper Cretaceous age. The Williams Fork consists of alternating beds of sandstone, sandy shale, carbonaceous shale and coal. The coal to be mined lies within a 392-foot interval in the Fairfield Member of the Williams Fork Formation. The quality of the coal seams is midway between bituminous and sub-bituminous. 9,000 feet of Mesozoic and 4,500 feet of Paleozoic sediments underlie these coal beds. The Williams Fork Formation is estimated to be 1,600 feet thick in the permit area and is underlain by the ridge-forming Trout Creek Sandstone member of the Iles Formation. Overburden material consists of a sequence of sedimentary claystones, siltstones, shales and carbonaceous-silty shales. These sediments are typical of the cyclothems deposited along the western interior of North America during Late Cretaceous time. The site-specific stratigraphy is Proposed Decision and Findings of Compliance 14 September 2009 Permit Renewal 05 Page 20